<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Stream-Oriented File Descriptors</title>
    <link rel="stylesheet" href="../../../boostbook.css" type="text/css">
    <meta name="generator" content="DocBook XSL Stylesheets V1.75.2">
    <link rel="home" href="../../../index.html" title="Asio">
    <link rel="up" href="../posix.html" title="POSIX-Specific Functionality">
    <link rel="prev" href="local.html" title="UNIX Domain Sockets">
    <link rel="next" href="fork.html" title="Fork">
</head>
<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
<table cellpadding="2" width="100%">
    <tr>
        <td valign="top"><img alt="asio C++ library" width="250" height="60" src="../../../asio.png"></td>
    </tr>
</table>
<hr>
<div class="spirit-nav">
    <a accesskey="p" href="local.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u"
                                                                                      href="../posix.html"><img
        src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png"
                                                                                            alt="Home"></a><a
        accesskey="n" href="fork.html"><img src="../../../next.png" alt="Next"></a>
</div>
<div class="section">
    <div class="titlepage">
        <div>
            <div><h4 class="title">
                <a name="asio.overview.posix.stream_descriptor"></a><a class="link" href="stream_descriptor.html"
                                                                       title="Stream-Oriented File Descriptors">Stream-Oriented
                File Descriptors</a>
            </h4></div>
        </div>
    </div>
    <p>
        Asio includes classes added to permit synchronous and asynchronous read
        and write operations to be performed on POSIX file descriptors, such as
        pipes, standard input and output, and various devices.
    </p>
    <p>
        These classes also provide limited support for regular files. This support
        assumes that the underlying read and write operations provided by the operating
        system never fail with <code class="computeroutput"><span class="identifier">EAGAIN</span></code>
        or <code class="computeroutput"><span class="identifier">EWOULDBLOCK</span></code>. (This assumption
        normally holds for buffered file I/O.) Synchronous and asynchronous read
        and write operations on file descriptors will succeed but the I/O will
        always be performed immediately. Wait operations, and operations involving
        <code class="computeroutput"><span class="identifier">asio</span><span class="special">::</span><span
                class="identifier">null_buffers</span></code>, are not portably supported.
    </p>
    <p>
        For example, to perform read and write operations on standard input and
        output, the following objects may be created:
    </p>
    <pre class="programlisting"><span class="identifier">posix</span><span class="special">::</span><span
            class="identifier">stream_descriptor</span> <span class="identifier">in</span><span class="special">(</span><span
            class="identifier">my_io_context</span><span class="special">,</span> <span class="special">::</span><span
            class="identifier">dup</span><span class="special">(</span><span class="identifier">STDIN_FILENO</span><span
            class="special">));</span>
<span class="identifier">posix</span><span class="special">::</span><span
                class="identifier">stream_descriptor</span> <span class="identifier">out</span><span
                class="special">(</span><span class="identifier">my_io_context</span><span
                class="special">,</span> <span class="special">::</span><span class="identifier">dup</span><span
                class="special">(</span><span class="identifier">STDOUT_FILENO</span><span class="special">));</span>
</pre>
    <p>
        These are then used as synchronous or asynchronous read and write streams.
        This means the objects can be used with any of the <a class="link" href="../../reference/read.html"
                                                              title="read">read()</a>,
        <a class="link" href="../../reference/async_read.html" title="async_read">async_read()</a>, <a class="link"
                                                                                                       href="../../reference/write.html"
                                                                                                       title="write">write()</a>,
        <a class="link" href="../../reference/async_write.html" title="async_write">async_write()</a>, <a class="link"
                                                                                                          href="../../reference/read_until.html"
                                                                                                          title="read_until">read_until()</a>
        or <a class="link" href="../../reference/async_read_until.html" title="async_read_until">async_read_until()</a>
        free functions.
    </p>
    <h6>
        <a name="asio.overview.posix.stream_descriptor.h0"></a>
        <span><a name="asio.overview.posix.stream_descriptor.see_also"></a></span><a class="link"
                                                                                     href="stream_descriptor.html#asio.overview.posix.stream_descriptor.see_also">See
        Also</a>
    </h6>
    <p>
        <a class="link" href="../../reference/posix__stream_descriptor.html" title="posix::stream_descriptor">posix::stream_descriptor</a>,
        <a class="link" href="../../examples/cpp03_examples.html#asio.examples.cpp03_examples.chat">Chat example
            (C++03)</a>,
        <a class="link" href="../../examples/cpp11_examples.html#asio.examples.cpp11_examples.chat">Chat example
            (C++11)</a>.
    </p>
    <h6>
        <a name="asio.overview.posix.stream_descriptor.h1"></a>
        <span><a name="asio.overview.posix.stream_descriptor.notes"></a></span><a class="link"
                                                                                  href="stream_descriptor.html#asio.overview.posix.stream_descriptor.notes">Notes</a>
    </h6>
    <p>
        POSIX stream descriptors are only available at compile time if supported
        by the target operating system. A program may test for the macro <code class="computeroutput"><span
            class="identifier">ASIO_HAS_POSIX_STREAM_DESCRIPTOR</span></code> to determine
        whether they are supported.
    </p>
</div>
<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%">
    <tr>
        <td align="left"></td>
        <td align="right">
            <div class="copyright-footer">Copyright © 2003-2022 Christopher M. Kohlhoff<p>
                Distributed under the Boost Software License, Version 1.0. (See accompanying
                file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
            </p>
            </div>
        </td>
    </tr>
</table>
<hr>
<div class="spirit-nav">
    <a accesskey="p" href="local.html"><img src="../../../prev.png" alt="Prev"></a><a accesskey="u"
                                                                                      href="../posix.html"><img
        src="../../../up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../home.png"
                                                                                            alt="Home"></a><a
        accesskey="n" href="fork.html"><img src="../../../next.png" alt="Next"></a>
</div>
</body>
</html>
